That's it, you've got it! Great, now you've exposed our secrets, how are we gonna be able to charge like bandits henceforth?
In real life, if you want to max out your lathe, you might make good use of an amperage meter, because otherwise, the proper load is a whole lot of guesswork.
The rigidity of the setup will also act as an unexpected factor to wreck the theoretical figures, as will the actual chip breaking abilities of a particular type of insert and material. Varying feedrates and depth of cut to force proper chip control is done quite often.